The TATA Binding Protein (TBP) is one subunit of distinct general transcription factors required by all three nuclear RNA polymerase enzymes. Each factor is formed by the binding of a distinct set of TBP Associated Factors (TAF's) to TBP. A number of human and viral proteins that bind TBP, including the p53, myc and E1A proteins, have been implicated in transcriptional control and tumorigenesis. Thus, an understanding of the means by which proteins bind TBP and regulate gene expression will have broad implications on diverse biological processes including growth control and cancer. We propose to investigate the mechanism by which the Stdl protein regulates gene expression as a paradigm for other transcriptional regulators that bind TBP. The STDl gene was isolated in my lab as an extragenic suppressor of a dominant negative mutation in TBP. Stdlp directly binds TBP as determined in both genetic and biochemical assays. We will investigate the effect of Stdlp on the DNA bi nding activity of TBP and the mechanism by which Stdlp activates transcription of the SUC2 gene in vivo.